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Question
When seen from below, the blades of a ceiling fan are seen to be revolving anticlockwise and their speed is decreasing. Select the correct statement about the directions of its angular velocity and angular acceleration.
Options
Angular velocity upwards, angular acceleration downwards.
Angular velocity downwards, angular acceleration upwards.
Both, angular velocity and angular acceleration, upwards.
Both, angular velocity and angular acceleration, downwards.
Solution
Angular velocity downwards, angular acceleration upwards.
Explanation:
As seen below, the fan is rotating in the anticlockwise direction; therefore, by the right-hand thumb rule, the direction of the angular velocity vector is towards the observer. Therefore, the angular velocity vector points downward.
The speed of rotation of the fan decreases in the anticlockwise direction; therefore, the angular acceleration is in the opposite direction. Therefore, the angular acceleration vector points upwards.
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